1. Field of the Invention
The present invention relates to wastewater treatment systems and methods, and, more particularly, to such systems and methods for wastewater treatment that are nonchemically based.
2. Description of Related Art
Wastewater treatment via xe2x80x9cnaturalxe2x80x9d means, i.e., without the addition of chemicals, has been accomplished with the use of aquatic and emergent macrophytes (plants) that, in concert with the attendant microorganisms and macroorganisms associated with macrophyte roots and stems, substantially mineralize biodegrade organic materials and substantially remove certain excess nutrients, such as nitrogen and, to a lesser extent, phosphorus. These macrophytes have typically been located in artificial marshlands, also known as constructed wetlands, which are designed for gravity flow. A negative aspect of such systems is that they are very land-intensive, requiring roughly on the order of 100 times as much land area as a conventional treatment plant, or, in terms of capacity, as much as 30-40 acres per 106 gallons of wastewater treated per day unless other treatment processes are incorporated into the constructed wetlands.
Subsurface-flow wetlands, which comprise aquatic plants positioned above a gravel filter, are also known for use in wastewater treatment. These systems have been shown to frequently fail, however. Failure is manifested as the upstream gravel tends to become clogged with biosolids, permitting the influent to bypass the clogged region and pass substantially untreated to a downstream region. Additionally, surface wastewater is a breeding ground for disease vectors and nuisance insects. Ultimately the gravel becomes so clogged that design wastewater treatment is substantially compromised. Plants also appear to have little treatment role in subsurface flow wetlands because the plant root systems are inhibited by conditions in the gravel filter from growing sufficiently long to extend into the gravel, and thus have minimal contact with the influent.
Several varieties of aquatic and emergent macrophytes are known to be used in wetland and aquatic wastewater treatment systems, including, but not limited to, cattails, bulrushes, sedges, and water hyacinths. In wetland treatment systems these plants may be packed in unlined or lined trenches or basins filled with a granular porous medium such as gravel or crushed stone. It has also been suggested to use recycled, shredded scrap tires in the place of the gravel. Another suggested wetland system variant is to place a semipermeable barrier between a lower level into which effluent enters and the plant root system for directing the wastewater flow across the entire plant bed.
In yet another variant, floating aquatic macrophytes, typically water hyacinths, are placed in shallow lagoons where plant roots, with attendant microorganisms and macroorganisms, extending into the water column are a principal design treatment mechanism. Although this root zone treatment method can provide advanced secondary treatment effluent, its application is limited by climate and available sunlight to approximately 5% of the United States. The large treatment footprint of water hyacinth treatment systems prohibits enclosure in greenhouses for almost all economically viable applications.
It is also known to combine plant root zone treatment with conventional activated sludge technology. The principal advantages of combining root zone treatment with activated sludge are improved nutrient removal capability over root zone treatment alone and improved treatment stability in small, activated sludge treatment systems. Among the problems encountered with root zone/activated sludge technology is that the clarifiers employed do not scale well when the size of the system is reduced beyond a certain point. In addition, operator qualifications are high for activated sludge systems, adding to the expense of running the system. Root zone/activated sludge technology has been known to digest in situ a large fraction of the biosolids produced and maintained within the treatment system, thereby reducing system biosolids yield. The mechanism for yield reduction is thought to be the retention of biosolids flocs on plant roots with subsequent consumption and mineralization of flocs by the invertebrate community attendant to the root zone. Reduction of yield is desirable only to a certain point, however. As reactors in series are added, thereby increasing biosolids contact with the root zone, yield may be reduced to the point where an insufficient quantity of biosolids remains to be recycled from the clarifier to the reactors in series. Lack of recycled biosolids substantially degrades the treatment performance of the activated sludge treatment element. This design trap is inherent to root zone/activated sludge treatment systems.
Preliminary studies have been performed on various aspects of the present invention by the inventors and other colleagues, and these have been reported in xe2x80x9cFinal Report on the South Burlington, Vt. Advanced Ecologically Engineered System (AEES) for. Wastewater Treatment,xe2x80x9d D. Austin et al., 2000; and xe2x80x9cParallel Performance Comparison between Aquatic Root Zone and Textile Medium Integrated Fixed Film Activated Sludge (IFFAS) Wastewater Treatment Systems,xe2x80x9d D. Austin, Water Environment Federation, 2001; both of these documents are incorporated herein by reference in their entirety.
The present invention provides a wastewater treatment system and method that are less land intensive than previous systems, as well as combining the advantages of a plurality of remediation techniques. The present invention has a smaller footprint than previously disclosed wetlands, reduces undesirable characteristics of an influent, and has a low yield, i.e., low proportion of matter needing disposal.
An additional feature of the invention provides a unified environment that includes a remediation system, as well as a method of doing business incorporating the water treatment systems of the present invention.
The wastewater treatment systems and methods of the present invention are amenable to the treatment of, for example, but not intended to be limited to, domestic wastewater, industrial waste or process water, urban runoff, agricultural wastewater or runoff, and even biological sludges. The systems are capable of handling a flow range of approximately 2000-2,000,000 gal/day. The types of contaminants that can be treated in the system include suspended particles, nutrients, metals, simple organics (oxygen-demanding substances), and synthetic or complex organics. The undesirable characteristics typically desired to be remediated include, but are not intended to be limited to, average biological oxygen demand (BOD), average total suspended solids (TSS), total nitrogen, and concentration of oil and grease. The systems of the present invention can reduce BOD to  less than 10 mg/L, TSS to  less than 10 mg/L, and total nitrogen to  less than 10 mg/L.
The water treatment system of the present invention comprises a wastewater inlet, a treated water outlet, and a plurality of treatment modules between the inlet and the outlet. Each module is for treating the water with a selected process. Each module is in fluid communication with at least one other module for permitting sequential treatment of the wastewater by a plurality of processes.
Influent wastewater is first directed to a covered anaerobic reactor, which serves to perform an initial organic and solids removal. In this vessel the solids from the influent settle, and anaerobic bacteria feed on the solids and wastes in the liquid. A filter is provided for removing odors from gases that are produced herein.
A first embodiment of the present invention includes a system for advanced treatment of wastewater. This system comprises an attached growth pretreatment filter that is at least intermittently exposed to atmospheric oxygen. The filter has an inlet for receiving water to be treated.
Following the filter are a first and a second hydroponic reactor, each having an inlet and an outlet. Hydroponic reactors are aerated reactors that have a rigid rack set at the water surface to support plants that send down roots into the wastewater column. The rack preferably covers substantially the entire water surface. Plants preferably substantially cover the entire surface of the rack.
A vertical-flow wetland comprises a basin having an outlet in a bottom thereof, and comprises a plurality of treatment regions through which the water to be treated passes under gravity flow. The basin is adapted to contain a particulate medium, and a mat positioned above the particulate medium is adapted for permitting plants to root therein. The wetland cell is adapted to maintain a population of aquatic invertebrates therein. Water entering the top of the vertical-flow wetland thus passes through a treatment zone formed by the plant roots. Beneath the root zone lies the particulate medium, such as, for example, an expanded shale aggregate for phosphorus absorption, solids filtration, nitrification, and BOD removal.
Water is transferred from the filter outlet to the first reactor inlet, and from the first reactor outlet to the second reactor inlet, and further is distributed from the second reactor outlet across at least a portion of the vertical-flow wetland.
If desired or necessary, water emerging from the vertical-flow wetland may be recycled either to the anaerobic reactor or to the filter for additional treatment. The final effluent may be subjected to additional treatment such as ultraviolet disinfection. The water emerging from the system is then suitable for reuse.
A second embodiment of the system is also directed to a system for advanced treatment of wastewater. This system also comprises an attached growth pretreatment filter that is at least intermittently exposed to atmospheric oxygen. The filter has an inlet for receiving water to be treated.
The system further comprises a first and a second tidal vertical-flow wetland (TVFW). The TVFW can be constructed in a plurality of configurations, and can include a first lagoon that has an inlet for receiving wastewater to be treated and a first vertical flow wetland cell that has an outlet adjacent a bottom thereof. A first means for transporting water from the first lagoon to the first wetland cell is provided.
The TVFW can also include a second lagoon that has an inlet for receiving water from the first wetland cell outlet and a second vertical flow wetland cell that has an outlet adjacent a bottom thereof. A second means for transporting water from the second lagoon to the second wetland cell is provided.
Means for recycling at least a portion of the water exiting the second wetland cell outlet to the first lagoon can also be provided.
Throughout the subsequent discussion, the definitions of lagoon and wetland cell will be generally taken as follows: The first and the second lagoon are adapted to function essentially aerobically and to contain plants having roots positioned to contact water flowing thereinto. The first and the second wetland cell are adapted to contain plants having roots positioned to contact water flowing thereinto.
The integrated TVFW treatment system of the present invention in a particular embodiment includes alternating wetland cells and lagoons. The overall hydraulic regime in this system involves fill and drain cycles wherein wastewater is alternately pumped between cells and lagoons. The vertical flux of water in and out of the wetland cells is designed to cycle over a predetermined period, and is therefore referred to as tidal.
It is to be understood that reference to first and second wetland cells or lagoons in no way limits the total number of wetland cells or lagoons in series. In embodiments where several wetland cells and lagoons are employed the flow regime is a logical serial extension of the flow described herein between the fist and second lagoon/wetland cell pair. For example, recycle flow from the second lagoon wetland cell pair is understood to represent recycle from the final lagoon/wetland cell pair.
Hydraulic design integrates passive forward flow, tidal flow, and recycle flow into one system. The process design in various embodiments integrates wetland and lagoon treatment technology. The process design of the present invention also includes elements of environmental and ecological engineering design that significantly improve the state of the art of wastewater treatment in general, and wetland wastewater treatment in particular.
In the TVFW, wastewater to be treated is subjected to a first substantially aerobic environment containing aquatic invertebrates for a first time period and is transported from the first aerobic environment to a surface of a first substantially anaerobic/anoxic environment containing plants having roots for a second time period. Aquatic invertebrates consume a substantial fraction of biomass produced within the system.
Water emerging from beneath the plant roots of the first anaerobic/anoxic environment is next transported to a second substantially aerobic environment containing aquatic invertebrates for a third time period. Water from the second aerobic environment is then transported to a surface of a second substantially anaerobic/anoxic environment containing plants having roots for a fourth time period. Aquatic invertebrates consume a substantial fraction of biomass produced within the system.
At least a portion of the water emerging from beneath the plant roots of the second anaerobic/anoxic environment is then recycled to the first aerobic environment.
Water is distributed from the filter outlet across at least a portion of a surface of the first wetland and also from a bottom of the first wetland across at least a portion of a surface of the second wetland. Water is also recycled from a bottom of the second wetland to a location downstream of the filter.
If desired or necessary, water emerging from the second TVFW may be recycled either to the anaerobic reactor or to the filter for additional treatment. The final effluent may be subjected to additional treatment such as ultraviolet disinfection. The water emerging from the system is then suitable for many reuse applications requiring wastewater treated to advanced standards. The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.